The present invention relates to an image display device that can improve uniformity of brightness and chromaticity on a display screen.
Accompanying the development of ever larger display screens in recent years, not only conventional direct viewing televisions of a CRT system, but various display devices such as a CRT projector, a liquid crystal projector and a plasma display have come into the market. In these image display devices, high screen uniformity of brightness and chromaticity is demanded according to their use. As an example, the liquid crystal projector will be discussed here. Accompanying the development of ever larger display regions, there is a problem of a poor uniformity such as brightness unevenness and color unevenness on a screen, resulting from unevenness of the characteristics of a light source constituting the device, an optical system and a liquid crystal as an image display element. Accordingly, it has become necessary to incorporate a circuit for correcting the poor uniformity due to the combination of above factors into the image display device. For example, JP 61-243495 A describes one technique. The following is a description of a structure of the conventional example mentioned above, with reference to a block diagram of an image display device shown in FIG. 10.
In FIG. 10, a video signal that is input from a video signal input terminal 1 is converted to video signals of primary colors of R, G and B by a signal processing circuit 2. The input video signal is input also to a synchronous separation circuit 8, and a horizontal synchronization signal and a vertical synchronization signal are separated therefrom. The separated horizontal synchronization signal is input to a phase-locking circuit 9, which generates a clock that is phase-locked with the horizontal synchronization signal. The clock and the vertical synchronization signal are input to an address counter 65, and correction data recorded in a memory 64 based on calculated address data are read out. This correction data are converted to an analog value by a D/A conversion circuit 62, and this analog correction value is added to the input video signal by using an adding circuit 61 so as to obtain a video signal, which drives an image display device, for example, a liquid crystal panel.
Recording the correction data in the memory 64 involves the following steps. First, a video signal with a constant level is input to the image display device so as to display the corresponding image on the screen Next, at each block that is formed by dividing the display screen suitably, its brightness level is measured by an image pickup camera, and direct current difference data from an aimed brightness level are recorded in the memory 64 as brightness correction data. The memory 64 in which the correction data are recorded is incorporated into a brightness correction circuit in the image display device. This correction data is read out by calculating an address of the memory corresponding to the display region divided when measuring the brightness, from the horizontal and vertical synchronization signals of the input signal. In this manner, the poor uniformity on the display screen is corrected.
However, this does not necessarily correct the brightness unevenness and the color unevenness in the entire region ranging from a low-brightness (near a black level) video signal input to a high-brightness (near a white level) video signal input, because the brightness measurement that serves as a basis of the correction data is carried out at a constant brightness level.
In order to solve the problem described above, the basic structure of the image display device of the present invention includes a first look-up table memory for correcting a gamma curve of an input video signal so as to correct a gradation of a display image, a second look-up table memory for generating uniformity correction data on a screen at each gradation level, a positional information generating portion for generating uniformity correction data corresponding to a position on the screen, a uniformity correction data making portion for synthesizing the correction data output from the second look-up table memory and the correction data output from the positional information generating portion, and an arithmetic processing circuit for correcting the video signal that has been subjected to the gradation correction and read out from the first look-up table memory by using the uniformity correction data output from the correction data making portion. The uniformity correction of the display image is performed at all gradation levels.
With the above structure, the uniformity correction according to the image display position at each gradation level of the input video signal is made possible. At the same time, it is possible to display an image without the brightness unevenness and the color unevenness in the entire region ranging from a low-brightness (near a black level) video signal input to a high-brightness (near a white level) video signal input.
In the above basic structure, it is desired that the positional information generating portion includes a first memory for retaining the uniformity correction data in a horizontal direction of the display image, a second memory for retaining the uniformity correction data in a vertical direction, a timing generating circuit for generating addresses to be input to the memories, and an arithmetic portion for calculating a positional information of the uniformity correction data from outputs of the first memory and of the second memory. This enables the reduction of a memory capacity, achieving both high precision and low price.
Also, as another example, the positional information generating portion can have the structure including a first memory for retaining the uniformity correction data in a horizontal direction of the display image, a second memory for retaining the uniformity correction data in a vertical direction, a timing generating circuit for generating addresses to be input to the memories, a low-pass filter for smoothing the output of the first memory and an arithmetic portion for calculating positional information of the uniformity correction data from outputs of the low-pass filter and of the second memory. This enables the reduction of a memory capacity, achieving the structure at still lower cost.
Furthermore, the image display device of the above basic structure may embody the following variation. That is, the image display device further includes a correction position setting portion for setting a uniformity correction position including a correction position setting input means, a CPU for converting horizontal and vertical positional information to binary information based on an input from the correction position setting input means, and horizontal and vertical position setting portions in which the positional information converted to the binary information by the CPU is written and retained. In addition, the positional information generating portion includes a timing generating circuit for generating addresses corresponding to the horizontal and vertical positions of the image, two functional arithmetic portions for calculating the horizontal and vertical address signals as one input and set values of the horizontal and vertical position setting portions as the other input, and an arithmetic portion for calculating a positional information of the uniformity correction data from outputs of the two functional arithmetic portions. This structure achieves a memory reduction, leading to a cost reduction. At the same time, the correction position setting portion for setting the uniformity correction position can achieve a uniformity adjustment with a simple setting of the correction position.
In the above basic structure, a correction amount interpolating arithmetic portion including an interpolating arithmetic portion and an adding arithmetic portion can be provided subsequent to the second look-up table memory, so that the correction amount interpolating arithmetic portion outputs a correction data in which the uniformity correction data is interpolated. With the interpolation, it is possible to reduce memory, as well as to adjust a uniformity correction in a gradation direction in a simple manner.
Furthermore, the image display device of the above basic structure may embody the following variation. That is, the image display device further includes a correction position setting portion for setting a uniformity correction position including a correction position setting input means, a CPU for converting horizontal and vertical positional information to binary information based on an input from the correction position setting input means, and a plurality of horizontal and vertical position setting portions in which the positional information converted to the binary information by the CPU is written and retained. In addition, the positional in format ion generating portion includes a timing generating circuit for generating addresses corresponding to the horizontal and vertical positions of the image, two functional arithmetic portions for calculating the horizontal and vertical address signals as one input and set values of the horizontal and vertical position setting portions as the other input, and an arithmetic portion for calculating a positional information of the uniformity correction data from outputs of the two functional arithmetic portions. A setting switching means of the horizontal and vertical positions switches the horizontal position setting for the uniformity correction at a vertical address timing and the vertical position setting for the uniformity correction at a horizontal address timing.
As described above, the uniformity correction in plural points is made possible by switching the horizontal position setting for the uniformity correction at the vertical address timing and the vertical position setting for the uniformity correction at the horizontal address timing respectively.